As shown in FIGS. 1 and 2, a conventional electrical magnetic switch includes an iron core 11, a coil 12 wound around the iron core 11, and an armature 13 detachably connected to the iron core 11. When the coil 12 is energized, an electrical current passes through the coil 12 so that the iron core 11 is magnetized to produce an electromagnetic effect. The armature 13 is magnetically attracted by the iron core 61 to be at a circuit-making position (as shown in FIG. 1), thereby forming a circuit with a relatively large electrical current flowing therethrough. When the coil 12 is de-energized, the electromagnetic effect of the iron core 11 disappears, and the armature 13 is placed at a circuit-breaking position (as shown in FIG. 2) to break the circuit. However, in order to maintain the circuit making position, the coil 62 has to be constantly energized. As a result, a hazard to use the conventional electrical magnetic switch may arise.
Referring to FIG. 3, a heart-shaped guide groove of a switch control unit provided in an electromagnetic relay assembly disclosed in Taiwanese Patent No. M485492 (a basic Taiwanese patent of a co-pending U.S. application of the applicant, i.e., U.S. patent application Ser. No. 14/665,152 filed on Mar. 23, 2015) is shown. The electromagnetic relay assembly has a switching unit controlled by the switch control unit, which is connected to an electromagnetic unit. The electromagnetic unit operates the switching unit through the switch control unit, and the switch control unit is able to lock the switching unit at a circuit-making and circuit-breaking position. Therefore, a need to constantly energize a coil of the electromagnetic unit for maintaining a circuit-making position of the switching unit may be dispensed with. The switch control unit has the heart-shaped guide groove 14 that is symmetrical to a reference axis (L1), and a locking member (not shown) inserted into the guide groove. The guide groove 14 enables a locking member (not shown) to slide cyclically therein in a counterclockwise direction and to be positioned at a lower first locking position 141 and a higher second locking position 142. The locking member slides from the first locking position 141 to the second locking position 142 and thereafter from the second locking position 142 to the first locking position 141 by consecutively passing through a first ramp 151, a first step 161, a second step 162, the second locking position 142, a third step 163, a second ramp 152 and a fourth step 164 for returning back to the first locking position 141. A gradient of the depth of the guide groove 14 is shown in FIG. 4. If each of the first, second, third, and fourth steps has a height of 0.2 millimeters along a direction of the depth of the guide groove 14, a largest depth gradient of the guide groove 14 is 0.6 millimeters. Because the guide groove 14 has a large depth gradient for the locking member to ascend and descend, not only does a greater kinetic energy be required to actuate the locking member to ascend in the guide groove 14 during the switching of the switch unit, but also the service life of the locking member may be reduced by impaction between the guide groove 14 and the locking member.